Annular-combustion-chamber bypass

ABSTRACT

An annular combustion chamber ( 1 ) for a gas turbine, the chamber having an outer shell ( 12 ) which has at least one inlet opening ( 4 ) for a burner ( 3 ) and an outlet ( 7 ) which opens into a turbine chamber ( 8 ), wherein ducts ( 14 ) which can be closed, which are oriented substantially parallel to the symmetry axis ( 2 ) of the annular combustion chamber ( 1 ), and through which final compressor air is guided into the annular combustion chamber ( 1 ) are provided in the outer shell ( 12 ) in the region of the outlet ( 7 ). Ring segments around the outer shell have projections selectively movable to at least partially block and open the ducts. A gas turbine is also disclosed.

The invention relates to an annular combustion chamber having a bypassfor reducing carbon monoxide emissions in partial load operation, and toa gas turbine having such an annular combustion chamber.

When the gas turbine is operated at partial load, the combustiontemperature in the combustion chamber drops. As a consequence, theprimary zone temperature which is relevant for carbon monoxide emissionsalso falls, to below a minimum value, whereby an increased quantity ofcarbon monoxide is generated and/or emitted. As this is to be avoided,the useful partial load range of the gas turbine is limited.

It is an object of the invention to provide an annular combustionchamber, of the type mentioned in the introduction, which permits aconsiderable increase in the useful partial load range.

The invention achieves this object by providing that, in such an annularcombustion chamber for a gas turbine, having an outer shell which has atleast one inlet opening for a burner and an outlet that opens into aturbine space, ducts are provided in the outer shell in the region ofthe outlet, which ducts are closable and are oriented substantiallyparallel to the axis of symmetry of the annular combustion chamber, andthrough these compressor outlet air can be guided into the annularcombustion chamber.

By virtue of this measure, it is possible to introduce compressor airinto a region at the end of the combustion chamber without it takingpart in the combustion, that is to say it is supplied back to theair-fuel mixture only after the combustion process. The effect of thisis that the richer mixture can be burnt in the combustion space athigher temperatures, and thus the carbon monoxide emissions duringpartial load operation can be reduced.

In one advantageous embodiment, the annular combustion chamber comprisesa last row of heat-shield plates arranged in the circumferentialdirection on the outer shell in the region of the outlet in the interiorof the annular combustion chamber, and a second-to-last row ofheat-shield plates arranged next to the last row in the direction of theat least one inlet opening, wherein a gap is provided between the lastand second-to-last rows of heat-shield plates, in the region of theducts. By virtue of this gap, the compressor outlet air can flowunperturbed into the combustion chamber.

It is further advantageous if an adjustment device, comprising ringsegments which form a ring that is oriented coaxially with the annularcombustion chamber and may be moved axially with respect to the annularcombustion chamber, is provided on the exterior of the outer shell forclosing and opening the ducts. The ring segments have the advantage ofsimpler assembly and/or disassembly.

In this context, it is expedient if the ring of the adjustment devicecan be moved in a continuously variable manner in order to set, asrequired, a desired gap width and thus to be able to remove a determinedquantity of air from the compressor outlet air prior to the combustion.

In one advantageous embodiment of the invention, the ring segments have,on their side facing away from the turbine, projections for engaging inthe ducts. In this context, it is expedient if the projections are oftrapezoidal design. By virtue of the projections, in particular byvirtue of their trapezoidal shape, the quantity of air to be guidedthrough the ducts can be set with particular precision. The ducts may ofcourse also be entirely closed. In that context, the ring is moved onlyin the axial direction, by a mechanism. Various possibilities exist forsuch a mechanism for controlling and moving the ring segments.Specifically, this can be effected using motors, lever or hydraulicmechanisms, etc., which for example displace the ring axially on railsor other movement elements. Optionally, these mechanisms may also beinstalled inside or outside the housing.

With regard to the high temperatures when the annular combustion chamberis in operation, it is advantageous if the projections of the ringsegments have a thermal barrier coating (TBC) on their surfaces exposedto the hot gas of the combustion. For the same reason, it is expedientif the interior of the outer shell also has a thermal barrier coating inthe region of the gap, between the last and the second-to-last rows ofthe heat-shield plates, that is to say between the openings of the ductsinto the interior of the combustion chamber. In annular combustionchambers according to the prior art, the last and the second-to-lastrows of the heat-shield plates still adjoin one another and the interiorof the outer shell was sufficiently protected by the heat-shield plates.The gap resulting from the invention increases the exposure of the outershell, in this region, to the hot gases of the combustion.

It is furthermore expedient if the last row of heat-shield plates, whichis the furthest of all the heat-shield plates from the core region ofthe combustion, is metallic and the second-to-last row is ceramic as, onone hand, the service temperature of ceramic materials is substantiallyhigher than the maximum service temperature of high-temperature metalalloys and, on the other hand, high-temperature metal alloys are lessbrittle and have better heat- and temperature-conducting behavior.

Finally, the invention also indicates a novel gas turbine in which anannular combustion chamber according to the invention is integrated.

By virtue of the continuously variable adjusting device according to theinvention for feeding compressor outlet air into a region at the end ofthe combustion chamber, i.e. after the combustion has taken place, it ispossible to reduce carbon monoxide emissions in partial load operationsince higher combustion temperatures arise on account of a richermixture.

The consumption of cold air in baseload operation is no greater thanwith current designs.

Furthermore, the invention is relatively easy to convert as the ringsegments, for example two half rings, are simple components which needonly be displaced axially.

The invention will be explained in more detail and by way of examplewith reference to the drawings, which are diagrammatic and not to scaleand in which:

FIG. 1 shows a combustion system having an annular combustion chamberaccording to the invention,

FIG. 2 shows the turbine-facing side of the annular combustion chamberwith adjustment device on the outer shell and bypass ducts,

FIG. 3 shows a half ring of the adjustment device for the bypass,

FIG. 4 shows a metallic heat-shield plate according to the prior art,

FIG. 5 shows a metallic heat-shield plate for the annular combustionchamber according to the invention and

FIG. 6 shows the interior of the annular combustion chamber in theregion of the outlet.

FIG. 1 shows, schematically and by way of example, the combustion systemof an annular combustion chamber 1 according to the invention. Theannular combustion chamber 1 consists of a closed ring which is arrangedaround a rotor axis 2. Burners 3 are arranged in inlet openings 4 in theupper region of the combustion chamber 1. This is where the fuel 5 ismixed with the compressor air 6. The actual combustion takes place inthe combustion chamber 1. The hot combustion gases enter the turbinespace 8 through the outlet 7 and there impinge upon the first staticguide vane 9. In order to protect against scaling, the annularcombustion chamber 1 is clad with ceramic heat-shields 10 and metallicheat-shields 11 which are attached to the outer shell 12.

According to the invention, the combustion chamber outer shell 12 isprovided with ducts 14 between the last ceramic heat-shield row 13 (i.e.the second-to-last heat-shield row) and the metallic intake shell plate(i.e. the last heat-shield row 11), in the region of the outlet 7, whichducts are oriented substantially parallel to the axis 2 of the annularcombustion chamber 1.

In order that these ducts 14 may be closed or opened as required, anadjustment device 15 is provided on the exterior of the outer shell 12,as shown in FIG. 2. The adjustment device 15 has ring segments 16, forexample two half rings, one of which is shown in FIG. 3. By means ofcorresponding projections 17, it is possible to set determined gapwidths in the ducts 14 or even to close the latter entirely.

In order to permit this inflow of air into the annular combustionchamber 1, the metallic intake shell plates, that is to say the platesof the last heat-shield row 11 are shorter than a heat-shield plate 18of the last row of an annular combustion chamber according to the priorart. FIG. 4 shows such a heat-shield plate 18 of the last row of anannular combustion chamber according to the prior art and the shorteningundertaken at the broken line so as to obtain a metallic heat-shieldplate 11 as shown in FIG. 5 and as required for the present invention.

FIG. 6 shows a view of the interior of the annular combustion chamber 1with last 11 and second-to-last 13 heat-shield plate rows and theopenings 20 of the ducts 14 in the outer shell 12 for the air bypassduring partial load.

Since, according to the invention, the last row 11 of the heat-shieldplates is shorter than the heat-shield plates according to the prior artand is arranged on the outer shell 12 of the annular combustion chamber1 such that it no longer directly adjoins the second-to-last row of theheat-shield plates 13, there results a gap 19 in the circumferentialdirection of the annular combustion chamber 1 without the heatprotection which exists hitherto. The ducts 14 open into the interior ofthe annular combustion chamber 1 in this gap 19. When the annularcombustion chamber 1 is in operation, the outer shell 12 is exposed tovery high temperatures between these openings 20. In order to protectthe outer shell 12 from these temperatures in spite of the gap 19, theinterior of the outer shell 12 is provided with a thermal barriercoating in the region of the gap 19 between the last 11 and thesecond-to-last row 13 of the heat-shield plates, that is to say betweenthe openings 20 of the ducts 14 toward the combustion chamber interior.

The projections 17 of the ring segments 16 also have a thermal barriercoating on their surfaces exposed to the hot gas of the combustion.

1. An annular combustion chamber for a gas turbine, the combustionchamber having an outer shell and the outer shell has at least one inletopening for a burner and has an outlet that opens into a turbine space;ducts in the outer shell located in the region of the outlet, the ductsare closable, the ducts are oriented substantially parallel to an axisof symmetry of the annular combustion chamber, and compressor outlet aircan selectively be guided through the ducts and into the annularcombustion chamber; an adjustment device, comprising a ring that isoriented coaxially with the annular combustion chamber and may be movedaxially with respect to the annular combustion chamber, the ring isprovided on the exterior of the outer shell and is configured andlocated for selectively closing and opening the ducts.
 2. The annularcombustion chamber as claimed in claim 1, comprising a last row ofheat-shield plates arranged in the circumferential direction on theouter shell in the region of the outlet from the interior of the annularcombustion chamber, and a second-to-last row of heat-shield platesarranged next to the last row in the direction toward the at least oneinlet opening a gap between the last and second-to-last rows ofheat-shield plates, in the region of the opening of the ducts into theinterior of the annular combustion chamber.
 3. The annular combustionchamber as claimed in claim 1, wherein the ring is movable in acontinuously variable manner for the selective closing and opening ofthe ducts.
 4. The annular combustion chamber as claimed in claim 1,wherein the ring has, on a side thereof facing away from the turbine,projections for engaging in respective the ducts.
 5. The annularcombustion chamber as claimed in claim 4, wherein the projectionsengaging in the ducts are of trapezoidal shape.
 6. The annularcombustion chamber as claimed in either of claim 4, wherein theprojections have a thermal barrier coating on surfaces exposed to hotgas.
 7. The annular combustion chamber as claimed in claim 6, whereinthe interior of the outer shell has a thermal barrier coating in theregion of the gap.
 8. The annular combustion chamber as claimed in claim2, wherein the last row of heat-shield plates is metallic and thesecond-to-last row of heat shield plates is ceramic.
 9. A gas turbinehaving an annular combustion chamber as claimed in claim
 2. 10. Theannular combustion chamber as claimed in claim 1, wherein the ring iscomprised of a plurality of ring segments which together define thering.